Hot wire welding and cladding are processes where a metal filler wire is resistively heated, typically, to a softened or plastic or semi-liquidus state, usually by passing an electrical current through it. This reduces the amount of added heat from another source needed for the base metal of a workpiece to which the heated wire is applied. The wire is typically fed in front of or behind a high-power energy source such as a laser or plasma that further melts the wire material, often along with the base metal of the workpiece, to produce a weld or clad. This puddle can also be referred to as the welding or cladding spot.
Wire feeders are used in various welding and cladding applications to feed the wire to the welding or cladding spot. Such wire can be referred to as filler wire, additive wire or consumable wire.
During operation, the wire is fed into or near the puddle. This way, when a workpiece is moved relative to the welding or cladding arrangement (with either the workpiece moved or the welding or cladding equipment moved), the puddle can be maintained to create a continuous weld or cladding layer.
In hot wire welding, the start of wire feeding is sequenced very precisely to prevent arcing, or overfeeding of the wire before the process can stabilize and be in a steady state. Commonly, first the wire feed is initiated. Second, the wire contacts the workpiece. Third, heating power (e.g., electrical current applied through the wire, which has some resistance) is applied to the wire. Fourth, the wire heats to a softened/plastic/semi-liquidus phase at the weld/clad spot, namely the weld/clad puddle. Fifth, feeding and sustained high power energy heating of the wire occurs in the steady state.
The use of hot wire welding, such as tungsten inert gas welding, tends to be more part-related and industry-related. For example, hot wire TIG is used extensively in the transportation and power generation industries. It's big in shipbuilding, and for rebuilding turbine shafts for large power plants. Hot wire TIG also is used in cladding very large valve welds such as those for oil industry in which welders clad the inside of the valve weld with high-performance alloys.
Current hot wire welding and cladding machines rely on welding voltage and current to control the process of resistively heating a wire. These parameters may also be used to calculate power, resistance, and extension. It is important to control the resistive heating process so that the wire is heated to sufficient temperature but also so that an arc is not generated between the wire and the workpiece. The temperature of the wire should be high enough that the wire plastically deforms at its end. However, if the temperature is too high, the end of the wire will turn liquid and electromagnetic pinch forces can cause an arc to be established. Arcing will disrupt the precise resistive heating going into the wire, can cause inconsistencies throughout the weld, and will require eye protection from the arc rays. Arcing can also be detrimental to cladding processes by causing considerable base metal melting, thus influencing the dilution of the cladding. The process of starting the welding or cladding operation is particularly prone to arcing.
When controlling the hot wire process to avoid arcing by relying on voltage and current feedback, information about the particular type of wire that is being used is necessary. Since different wire types have different parameters, such as melting temperature, electrical resistivity, heat capacity, and thermal conductivity, each wire type requires its own program or input of particular parameters into the welding or cladding machine in order to ensure successful operation.